Skip to Content

How to Charge Car Audio Capacitor in Less than 5 Minutes?

When upgrading car audio, you may need to add a capacitor to the system. However, before the first connection, a capacitor has to be charged.

Although charging is not complicated, there are some tricks, so I decided to create a short article about how to charge capacitors for car audio.

TedsWoodworking Plans and Projects

As a general rule, when charging a capacitor, wire its positive terminal to the positive terminal in the car battery and add a resistor between both terminals. The resistor adds a load to the circuit so the capacitor can be charged. Then connect the capacitor’s negative terminal to the ground chassis, but not to the same place as the amplifier.

As an Amazon Associate, ImproveCarAudio will receive a small commission from qualifying purchases made through the links in this article.

Tip: A capacitor can be charged to the maximum battery voltage level. For example, a typical 12V battery will charge the capacitor to no more than 12V, and it does not matter if your capacitor is 1F or 18F.

For most car sound systems, capacitors between 2F and 5F will be sufficient, with my favorite for the money, SoundBox 2.5F SCAP2D

In the article below, I will go through more details and different ways of charging audio capacitors, depending on the system installed.

Do You Need a Capacitor for Sound System?

From storing electric charges to controlling reactance, capacitors have a critical role in circuits. Capacitors are advantageous over batteries since they charge in less time. However, capacitors store a relatively tiny amount of energy.

In vehicles, having a high-pitched audio system is excellent. However, amplifiers draw a large amount of power from the battery, leaving other car features inadequate. In some instances and with strong amplifiers installed, driving during the night becomes risky due to dimming lights.

Besides, other elements in the vehicle are subject to complete damage. A capacitor comes in handy to avoid straining the alternator and battery.

how to charge car capacitor

A powerful capacitor allows the alternator to run all the activities from starting the engine to powering the audio. There are three types of car audio capacitors:

  • carbon
  • electrolytic
  • hybrid

The three vary in terms of the energy they can contain. An electrolytic capacitor has a fast charge rate but holds a relatively low amount of power.

In contrast, carbon capacitors hold more power but take a longer time to charge. A hybrid capacitor is a blend of carbon and an electrolytic capacitor.

Do Capacitors Need to Be Charged?

If stored in a charged state, the Capacitors may remain charged even after removal from a circuit. The charge is dangerous and may also lead to fatal shock.

Large capacitors require that the terminals are shorted before storage because there is potential to develop high voltages when the circuit is left open. Therefore, a new capacitor is not ready for use once you purchase it from the factory.

You have to charge the capacitor before installing it into the audio system; otherwise, the rapid current inflow will lead to a spark.

What Does a Capacitor Do for Car Audio?

Without a capacitor, there is an imbalance in the supply of power. If the model of your amplifier consumes a lot of energy, it will compete with the lights dim when the music plays. Driving at night could lead to accidents due to poor visibility.

If you are driving with the music on, you may be distracted by the unexpected flashing of headlights. Without a capacitor, the audio system takes a large amount of power, leaving the battery to maintain the lights in a constant state.

A capacitor is necessary as it lets the amplifier take energy from it as the car battery concentrates its effort on the lighting.

What do I need to charge a capacitor?

Although there are no special tools needed, there are a few main items that become handy when connecting and charging capacitor:

  • Power Wire with the same size as for the rest audio system

How to Charge the Capacitor for Car Audio?

New capacitors come with a charging tool that is a simple plate with a resistor and four wires. Two wires you have to plug into positive and negative terminals in the capacitor. Another positive wire with a battery positive terminal and a second negative wire we ground to the car’s chassis.

It’s important to remember that you cannot connect the negative terminal to the audio system’s ground.

charging car audio capacitor

Below are a few steps on how to connect a capacitor with the car electrical system and charge it properly when it is not equipped with the original charging tool:

  • Park the vehicle on flat ground and apply the parking brake.
  • Plug in the memory saver.
  • Unplug the ground wire from the battery starting with the negative battery cable. When you begin by unplugging the positive wire, you may cause a short when you touch the vehicle. 
  • Take the wire you want to use for the positive connection. Ensure there is no fuse on this wire. Otherwise, it will be blown when you close the circuit.
  • Add connectors to the wires.
  • Connect the positive terminal on the capacitor to the audio system. Once the capacitor is connected, mount the capacitor to the vehicle.
  • Connect the capacitor’s negative terminal to the ground. Make sure you use a different point on the chassis than the existing amplifier’s connection.

Now capacitor starts to charge and, after few minutes, will be ready to begin supporting the audio system.

How Do You Charge a Car Capacitor Without a Resistor?

When you do not have a resistor to complete the charging circuit, you can still charge your capacitor by using a lightbulb. To use this method, you need to have additional elements:

With all tools in hand, take the steps below, and you will charge your capacitor with a light bulb in no time:

  • Place the capacitor close to the battery.
  • Connect the capacitor’s negative terminal to the car chassis.
  • Hold the test light by using alligator clips between the positive terminal of the battery and the positive terminal of the capacitor. Hold the test light for a few minutes. When the capacitor is charged, the test light bulb will turn off.

How Long Does It Take to Charge a Capacitor?

Charging time depends on its size, but it takes less than 5 minutes for the capacitor to be fully charged on average.

When comparing to the time needed for charging the battery, charging a capacitor is much faster.

How Do You Know When a Capacitor Is Fully Charged?

The easiest way to see if a capacitor is fully charged is to look at the current value at its voltmeter screen. However, there are several methods to determine if a capacitor is already charged when there is no digital display:

The capacitor, when it is fully charged and ready to be installed in the car, should have a voltage over 13V.

When using an external multimeter or voltmeter to check the capacitor’s charging level, you have to connect the red positive probe of the multimeter to the positive capacitor terminal and the negative probe to the negative terminal. The number shown on the screen will be the exact voltage of the capacitor.

How Many Times Can a Capacitor Be Charged?

Due to mechanical forces resulting from discharges, the components of capacitors, especially those of high energy storage, tend to deteriorate with time.

The capacitors thus have a threshold on the charging cycles. However, electrolytic capacitors can endure a large number of charging cycles compared to others.

What to Do When an Audio Capacitor Is Not Charging?

The audio capacitor may fail to charge if it is not in a complete circuit. Such a circuit must have a source of power, load, and path for the current to flow through. A circuit load may include a resistor or a test light bulb.

If your audio capacitor is damaged, the best option is to have a replacement.

How to Discharge Car Audio Capacitor?

The best way to discharge a car audio capacitor is by short-circuiting it for 30 minutes or more.

A car’s main car stereo amplifier must be turned off when discharging a capacitor because it can retain electric charge for hours upon hours, even after it has been fully discharged and unplugged from the power source.

After your capacitor has discharged, remember to disconnect wires from both terminals. Then, whether you still want to use the capacitor or not, you should clean it with rubbing alcohol before reinstalling or storing away if exposed to dirt, dust, or debris while being used.

How Fast Does a Car Audio Capacitor Discharge?

Car audio capacitors discharge very fast. They usually take only a few minutes for car audio capacitors to discharge completely.

The car’s alternator continues to supply voltage while the car’s engine is on and is continuously charging the car capacitor at the same time.

But if you turn off the car, the alternator stops working, and the capacitor starts to discharge. You can test this by touching some jumper cables onto the terminals of an old car battery.

It’s also important to note that car capacitors worsen as they age because they lose their ability to hold a certain volume of electric charge.

Some car audio capacitors start at 1F but after two years may only retain at most 0.8F due to aging. Aging in the audio capacitor also means that it takes longer to charge it fully.

Another thing to remember is that a car capacitor can fully recharge in around 30 minutes from when connected to a drained car battery.


One thing you never wish is to keep running to buy another car part now and then. Some critical features in your vehicle could be defective if the battery concentrates on running the audio system.

For instance, the alternator or even the battery itself could become defective. A powerful capacitor takes the responsibility of running the audio system as the battery power all the other stuff in the vehicle, and the alternator starts the engine.

However, it’s essential to be cautious in handling capacitors. Large capacitors can be fatal, especially when shorted. Remember also to discharge a capacitor before throwing it into the trash as it may cause a fire.